This invention relates to a method of passivating a semiconductor junction, and, more particularly, to such a method using a multi-layer passivant system.
A recently utilized passivant system for semiconductor junctions includes an oxygen doped polycrystalline silicon layer applied either directly on the semiconductor surface or over an oxide layer on the semiconductor surface. Over this polycrystalline layer there is applied an oxide layer, usually silicon dioxide (SiO.sub.2). For high voltage semiconductor devices, the passivant system may further include a thick glass layer over the oxide and yet another oxide layer over the glass.
The above described multi-layer passivant systems are highly effective, but are relatively expensive to utilize as can be seen from the following brief description of a most usual method of depositing the various layers on the semiconductor device. In accordance with the most usual technique, the oxygen doped polycrystalline silicon is deposited in a chemical vapor deposition (CVD) process wherein the wafer is placed in a CVD reactor which is heated to a temperature of between about 600.degree. C. and about 750.degree. C. Silane (SiH.sub.4) and nitrous oxide (N.sub.2 O) are then fed into the reactor in a suitable ratio (preferably from about 0.2 to about 0.4) and the silane and nitrous oxide react on the hot semiconductor surface to form a layer of polycrystalline silicon uniformly doped with oxygen atoms. Next, the oxide layer is deposited on the oxygen doped polycrystalline silicon layer by a low temperature CVD process. In carrying out this process, the wafer is placed in another CVD reactor in which the temperature is maintained at about 400.degree. C. to about 600.degree. C. and silane and oxygen are now fed into this reactor. The silane and oxygen react to deposit a layer of silicon dioxide over the surface of the polycrystalline silicon. Thereafter, the silicon dioxide is annealed at a temperature of about 900.degree. C. in a nitrogen atmosphere. Any additional layers to be deposited over the oxide are provided in accordance with generally conventional techniques. The numerous steps required to form the oxide layer over the polycrystalline silicon layer add significantly to the cost of the system.